1. Field of the Invention
The present invention relates to an engine natural vibration frequency detection method and apparatus for detecting a natural vibration frequency of a rigid body resonance of an engine supported through an active vibration isolation support device toga vehicle body; and an active vibration isolation support device control method and apparatus using the natural vibration frequency detection method.
Further, the present invention relates to an active vibration isolation support device which is disposed between a vibrating body and a supporting body, and is extended and retracted periodically by control means supplying current to an actuator so as to suppress the vibration of the vibrating body from being transmitted to the supporting body; and a vibrating body vibration frequency detection apparatus for detecting the vibration frequency of the vibrating body using the active vibration isolation support device.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 2005-3156 discloses an active vibration isolation support device which calculates a crank angular velocity from a time interval between crank pulses outputted every time a crankshaft rotates through a predetermined angle; calculates a crankshaft torque from a crank angular acceleration obtained by differentiating the crank angular velocity with respect to time; estimates an engine vibrational state as a torque variation; and controls the supply of current to a coil of the actuator according to the engine vibrational state, thus exerting a vibration isolation function.
The engine torque varies according to a crankshaft phase, and thus, as a reaction thereto, a roll moment so as to roll the engine body around the crankshaft also varies according to the crankshaft phase. The cycle in which the roll moment increases and decreases varies according to the engine rotation number. Therefore, when the cycle in which the roll moment increases and decreases matches the roll resonance frequency of an engine elastically mounted on the vehicle body at a specific engine rotation number, a vehicle body vibration occurs, causing a problem giving an unpleasant feeling to the driver or a passenger. Accordingly, the vibration due to a roll resonance needs to be suppressed by detecting the roll resonance frequency and operating the active vibration isolation support device at an engine rotation number range in which the roll resonance occurs.
However, in general, the roll resonance frequency is lower than the vibration frequency in an engine rotation number (an engine rotation number equal to or greater than an idling engine rotation number) in a normal operation range of an engine, and thus there is a problem in that the roll resonance frequency cannot be detected during the normal operation of the engine.